A thick film resistor composition widely used in thick film resistor electrical parts, thick film hybrid circuits, etc. is a composition for forming a resistor thick film by printing the composition on a conductor pattern or an electrode formed on the surface of an insulating substrate, and then calcining the print.
The thick film resistor composition is prepared by dispersing a conducting component and an inorganic binder in an organic medium (vehicle). The conducting component plays a principal role of determining the electrical properties of the thick film resistor, and a ruthenium oxide or the like is used as this component. The inorganic binder comprises glass, and has a major role of retaining the thick film integrally and binding it to the substrate. The organic medium is a dispersing medium that affects the application properties, particularly theology, of the composition.
When a thick film resistor composition is to be used for a hybrid microelectronic circuit or a chip resistor, it is important that the electric stability of the resistor be high, and especially changes in the temperature coefficients of resistance (TCR's) of a variety of resistors responsive to changes in their pad lengths (widths) be small. In recent years, the sizes of the resistors have varied widely from a minimum of, say, 0.3.times.0.3 mm to a size of several millimeters square according to the designs of the devices. When such a resistor is combined with a Pd/Ag electrode or an Ag electrode, however, the resistor with a small length will pose the problem that the shape of the resulting print or the film thickness obtained will change, or Ag or the like will diffuse from the electrode into the resistor. This will cause changes in the resistance and TCR of the resistor thick film. Even if the resistance varies slightly, it can be adjusted to a predetermined value, by laser trimming which removes a part of the resistor thick film with laser. The TCR, once varied, cannot be adjusted actively. Therefore, it is desired that the degree to which TCR, rather than resistance, depends on the pad length of the resistor be low, namely the length effect be low. TCR includes hot TCR (HTCR) and cold TCR (CTCR), and it is preferred that both HTCR and CTCR have a low length effect.
Improvements, such as changing the formulation and the proportions of components of the thick film resistor composition, have been tried in order to reduce the length effect of the TCR. However, no satisfactory results have been obtained.